Orthogonal frequency-division multiplexing (OFDM) is a modulation technique used at the physical layer (PHY) of a number of wireless networks, e.g., networks designed according to the IEEE 802.11a/g, and IEEE 802.16/16e standards. OFDMA is a multiple access scheme based on OFDM. In OFDMA, separate sets of orthogonal tones (subchannels) and time slots are allocated to multiple transceivers (users) so that the transceivers can communicate concurrently. As an example, the IEEE 802.16/16e standard, has adopted OFDMA as the multiple channel access mechanism for non-line-of-sight (NLOS) communications at frequencies below 11 GHz.
FIG. 1A shows a conventional OFDMA-based cellular network 100, e.g., a wireless network according to the IEEE 802.16/16e standard, incorporated herein by reference. The network confines operations to a point-to-multipoint topology, wherein only two types of network entity exist, namely base stations (BS), and mobile stations (MS). The BS manages and coordinates all communications with the MS in a particular cell on connections 101-103. Each MS is in direct communication with only the BS, and only the BS communicates with an infrastructure 110 or “backbone” of the network. That is, there is only one hop between the MS and the BS. All communications between the MS must pass through the BS. Furthermore, there is one connection between the BS and each MS.
Due to significant loss of signal strength along the connection for certain spectrum, the coverage area of wireless service is often of limited geographical size. In addition, blocking and random fading frequently results in areas of poor reception, or even dead spots. Conventionally, this problem has been addressed by deploying BSs in a denser manner. However, the high cost of BSs and potential increase in interference, among others, render this approach less desirable.
As shown in FIG. 1B for an alternative approach, a relay-based network 150 can be used. The network includes multiple mobile stations (MS) and/or subscriber stations (SS). A relatively low-cost relay station RS extends the range of the BS. Some of the stations (MS1 and SS1) communicate directly with the BS using connections C1 and C2. Other stations (MS2, MS3 and SS2) communicate directly with the RS using connections C3, C4 and C5, and indirectly with the BS via corresponding connections 151 using two hops. Obviously, communications on the link between the RS and BS (relay link) can become a bottleneck.
To improve efficiency, the manner of communicating between the relay and base station needs to be improved.